1. Field of Invention
The present invention relates to an optical disk write/read apparatus for writing data on the optical disk and for reading data from the optical disk and the optical disk write method by using a modulation of light power in writing data on the optical disk, more particularly, to an optical disk write/read apparatus for writing data on the optical disk and for reading data from the optical disk and its write method by modulating the laser power which is irradiated to optical disk by feeding a RF signal which is transformed from the reflection light reflected from the optical disk, so as to improve the characteristic of the pit generation in writing mode, back to a controller.
2. Discussion of the Related Art
A conventional optical disk write apparatus, as shown in FIG. 1, consists of laser diode 1 which is to write data on an optical disk and to read data from the optical disk, microcomputer 7 which sets up, according to the user command, the write/read power reference necessary to generate a pit and controls a system, a read controller 3 which is responsive to the read power reference of said microcomputer 7 and to a read control signal from an external encoder 11 and controls the laser emission of a laser diode 1 and the operation timing through a voltage-current converter 5, a write controller 4 which is responsive to the write power reference signal of said microcomputer 7 and a write control signal from an external encoder 11 and controls the laser emission of a laser diode 1 and the operation timing through a voltage-current converter 5', a monitor diode 2 which detects, in order to keep the change of the laser power within a certain range during the write and read modes, a reflection light reflected from the optical disk according to the emitted light of the laser diode 1 and feeds the detected signal back to the read controller 3 or a write controller 4, a temperature compensation circuit 6 which compensates the change of the emitted light of the laser according to the temperature change and makes a laser emission of constant power, quad photodiodes 9 in which four photodiodes receive the reflection light reflected from the optical disk 8 and convert the four light into four RF signals, and a RF amplifier 10 which adds said four RF output signals from said quad photodiodes 9 and amplifies the added signal.
In the conventional optical disk write/read apparatus, as described above, if a user inputs a command for writing (or reading) to the apparatus, microcomputer 7 generates the write (or read) power reference necessary to generate a pit according to said command and, by switching the laser diode 1 according to the waveform obtained from said write (or read) power reference and said encoder 11, writes data onto (or reads data from) the optical disk 8. During writing (or reading), a monitor diode 2 detects the reflection light reflected from the optical disk 8 according to the laser power emitted from a laser diode 1 and the detected signal is applied to the write controller 4(or the read controller 3). When a change of the present laser power is detected, the write controller 4 (or the read controller 3) is modified in order to compensate the change. Therefore, it is possible to prevent the write power (or the read power) from going out of a certain range because of any internal or external disturbances. If the laser power is changed according to temperature change during writing (or reading), the change of the laser power is detected by a temperature compensation circuit 6 and a signal corresponding to the laser power change is sent to the write controller 4 (or the read controller 3). The write controller 4 (or the read controller 3) is based on the signal and controls the laser power of the laser diode 1 to be constant in the writing (or reading) mode.
And the conventional optical disk write operation is done as follows:
As shown in FIG. 2A, in order to write a pit of a specified length on the optical disk 8, a write signal (a write pulse) V.sub.0 which turns on the laser diode 1 for the time .DELTA.t.sub.1 corresponding to the generation of the pit length, is generated by encoder 11. The write pulse V.sub.0 is applied to the write controller 4 under the control of a microcomputer 7 and then is transformed into a write current I.sub.0 through a voltage-current converter 5, as shown in FIG. 2B. The write current I.sub.0 is applied to the laser diode 1. When the write power of the laser is irradiated on the optical disk 8, the write power is reflected from the optical disk 8. The quad photodiodes 9 converts the reflection light reflected from the optical disk 8 into an RF signal V.sub.1, as shown in FIG. 2C. The RF signal V.sub.1 of the photodiodes 9 corresponding to the reflection light reflected from the optical disk 8 is a large signal in the early stage of the pit generation. After the pit is generated, the RF signal becomes a little smaller but it maintains a stable RF signal level. If the write material on the optical disk 8 is heated by the write power of the laser diode 1 and its temperature goes up to a threshold level, the phase change of the write material, for example, the change from a crystalline structure to an amorphous structure in a phase change material, occurs. As the result, a pit is generated. At this time, as shown in FIG. 2D, there are a time delay .DELTA.t.sub.2 corresponding to the absorption of heat necessary for a pit to be generated and a time delay .DELTA.t.sub.3 which is necessary for the width of the pit to be a stable value of W.sub.1.
Therefore, even though the write power of laser diode 1 is applied on the optical disk 8, the pit is not immediately generated on the optical disk 8 and a time delay (.DELTA.t.sub.2 +.DELTA.t.sub.3 ) which is necessary for the temperature of the write layer on the optical disk 8 to go up to a threshold level and to be stable exists.
Moreover, even though the write power is removed, the pit generation does not completely stop. There is a time delay .DELTA.t.sub.4 until the pit generation stops.
Because each optical disk, as shown in FIG. 2E, has the write layer or the reflection layer with a unique characteristic, even though a constant write power is applied to the optical disk 8, the RF signal levels according to the reflection light reflected from the optical disk 8 are V.sub.1, V.sub.2 and V.sub.3, not equal values like these. Therefore, as shown in FIG. 2F, the write pit generations are delayed by .DELTA.t.sub.5, .DELTA.t.sub.6 and .DELTA.t.sub.7, respectively, and each pit is different each other in its total length and the width of each pit is also different each other, for example W.sub.1, W.sub.2 and W.sub.3 in FIG. 2F.
As explained above, because the conventional optical disk write/read apparatus or the conventional write method uses always a constant rectangular laser power at any time after the completion of the pit as well as at the beginning of the pit generation, the pit edge is formed by the small heat energy being transferred into the optical disk at the early stage. Therefore, the jitter characteristic is too bad and the time necessary for the pit to be generated is long. Furthermore, because of the difference of the reflection coefficients in the pit generation, there are some problems of which each optical disk has different pit length each other and the width of the pit becomes comparatively wide.